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internal/manifest: document relationship between LastSeqNum and WAL seqnums #5534

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Nov 6, 2025
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internal/manifest: document relationship between LastSeqNum and WAL seqnums #5534

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3 changes: 2 additions & 1 deletion internal/manifest/version_edit.go
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Original file line number Diff line number Diff line change
Expand Up @@ -150,7 +150,8 @@ type VersionEdit struct {

// LastSeqNum is an upper bound on the sequence numbers that have been
// assigned in flushed WALs. Unflushed WALs (that will be replayed during
// recovery) may contain sequence numbers greater than this value.
// recovery) may contain sequence numbers greater than this value. They're
// also allowed to contain sequence numbers less than or equal to this value.
LastSeqNum base.SeqNum

// A file num may be present in both deleted files and new files when it
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6 changes: 6 additions & 0 deletions version_set.go
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Expand Up @@ -34,6 +34,12 @@ const manifestMarkerName = `manifest`
// to the MANIFEST file, which is replayed at startup.
type versionSet struct {
// Next seqNum to use for WAL writes.
//
// Note that unflushed WALs may contain sequence numbers less than, equal
// to, or greater than logSeqNum. This is because every version edit
// includes the current logSeqNum, so any version edits applied after a
// write and before the flush of the write to a sstable will update
// logSeqNum beyond the write's sequence number.
logSeqNum base.AtomicSeqNum

// The upper bound on sequence numbers that have been assigned so far. A
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